Synthetic method of glycol diesters from reaction of glycol monoesters and linear aliphatic carboxylic acids

ABSTRACT

A method of synthesizing glycol diester by reacting a linear aliphatic carboxylic acid and a glycol monoester in the presence of a Lewis acid type catalyst is provided. In the method, after introducing the glycol monoester, the linear aliphatic carboxylic acid and the Lewis acid type catalyst into a reactor, the reaction occurs to produce reaction products and water in the reactor; an excess of the linear aliphatic carboxylic acid forms an azeotrope with water during the reaction to be sent to a condenser through a distillation column; the linear aliphatic carboxylic acid and water passed through the condenser are divided into an organic layer and an aqueous layer in an oil water separator; and the organic layer is returned to the distillation column through a material cycling line and water in the aqueous layer is removed through a water removal line. By utilizing reactive distillation technique, water produced during the reaction is rapidly removed, and thus the reaction time can be significantly reduced and the yield of the glycol diester can be maximized.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of synthesizing a glycol esterrepresented by formula (3) from a glycol monoester represented byformula (1) and a linear aliphatic carboxylic acid represented byformula (2) in the presence of a Lewis acid type catalyst utilizingreactive distillation technique in which a reaction time can besignificantly reduced by rapidly removing water produced during thereaction:HO—R¹—O—C(═O)—R²  (1)R³—C(═O)—OH  (2)R³—C(═O)—O—R¹—O—C(═O)—R²  (3)where R¹ is a C₁-C₁₆ alkylidene group, R² is a C₁-C₁₆ alkyl group, andR³ is a C₃-C₁₆ linear alkyl group.

2. Description of the Related Art

Generally, in the case of the same molecular weight, glycol diestersproduced by the reaction between glycol monoesters and linear organicacids have superior physical properties than glycol diesters produced bythe reaction between glycol monoesters and branched organic acids due tophysical properties of the linear organic acids. For example, viscosity,migration-resistance in the application processing test of polymers suchas polyvinyl chloride (PVC), and etc.

Glycol diesters are produced through an ester reaction from alcohols andacids in the presence of catalysts, in which water is also produced as aby-product together with the desirable products. During the reaction,water increases over time. In the reversible ester reaction, due to thepresence of water, the reaction rate is reduced and the activity of theused Lewis acid catalyst is degraded. Thus, in order to reduce thereaction time by increasing the reaction rate, it is important torapidly separate and remove water produced during the reaction fromreactants. Studies on a method of removing water produced during thereaction, at fastest rate, have been conducted. Also, a method ofincreasing the yield of glycol esters by optimizing a catalyst andoperating conditions, etc. has also been studied. Conventionaltechnologies of synthesizing glycol diesters are as follows.

Japanese Patent Laid-Open Publication No. 49-94621 discloses thereaction of 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate andisobutyric acid using tetraisopropyl titanate as a catalyst. In themethod, xylene is used as a solvent and water produced during thereaction is removed using azeotropic distillation. In the publication,it is described that the reaction time is 18 hours which issignificantly shortened time compared to 24 hours required in otherconventional methods, and the yield of 2,2,4-trimethyl-1,3-pentanedioldiisobutyrate is 95%. However, this technology further requires aprocess of recovering the solvent after the reaction and does notachieve significant reduction in the reaction time.

In DE Patent No. 3,102,826, isobutyraldehyde is used as a startingmaterial and para-toluenesulfonic acid which is a strong acid is used asa reaction catalyst. As a result, the reaction is completed in onlyabout 4 hours. Although the reaction time is somewhat shortened, theselectivity to 2,2,4-trimethyl-1,3-pentanediol diisobutyrate is 78% andreaction process yield was low (61%).

U.S. Pat. No. 5,180,847 teaches that isobutyraldehyde is used as astarting material and an alkali metal hydroxide which is a strong baseis used as a catalyst to produce about 23% of2,2,4-trimethyl-1,3-pentanediol, about 28% of2,2,4-trimethyl-1,3-pentanediol monoisobutyrate and 41% of2,2,4-trimethyl-1,3-pentandiol diisobutyrate. In this case, three usefulcomponents can be simultaneously obtained, but when2,2,4-trimethyl-1,3-pentanediol diisobutyrate is desired as a finalproduct, the yield of the final product is low.

As described above, when a Lewis acid type catalyst is used to increasethe yield of glycol diester such as 2,2,4-trimethyl-1,3-pentandioldiisobutyrate, the reaction time is long. Meanwhile, when a strong acidor strong base catalyst is used to shorten the reaction time, theselectivity to glycol diester and the yield thereof are low. Thus, thereis a demand for a process capable of maximizing the yield of glycoldiester and shortening the reaction time.

The inventors of the present invention discovered that the selectivityto glycol diester can be maximized by using a Lewis acid type catalystwhich is a weak acid, for example, tetraisopropyl titanate,tetra-n-butyl titanate, tetra 2-ethylhexyl titanate, etc., and reactivedistillation through a distillation column installed in a reactor isutilized to effectively remove water produced during the reaction underthe condition that an excess of a linear aliphatic carboxylic acid isused, thereby achieving significant reduction in the reaction time.Thus, the present invention is completed.

SUMMARY OF THE INVENTION

The present invention provides a method of synthesizing a glycol diesterfrom a glycol monoester and a linear aliphatic carboxylic acid using aLewis acid type catalyst, in which the selectivity to the glycol diesteris maximized and the reaction time is significantly reduced, and a novelglycol diester obtained.

According to an aspect of the present invention, there is provided amethod of synthesizing a glycol diester, including reacting a linearaliphatic carboxylic acid and glycol monoester in the presence of aLewis acid type catalyst.

In the method, after introducing the glycol monoester, the linearaliphatic carboxylic acid and a Lewis acid type catalyst into a reactor,the reaction occurs to produce reaction products and water; an excess ofthe linear aliphatic carboxylic acid forms an azeotrope with water to besent to a condenser through a distillation column; the linear aliphaticcarboxylic acid and water passed through the condenser are divided intoan organic layer and an aqueous layer in an oil water separator; and theorganic layer is returned to the distillation column through a materialcycling line and water in the aqueous layer is removed through a waterremoval line.

The glycol monoester may be at least one compound selected from thegroup consisting of compounds having the structure represented by theformula (1) and the linear aliphatic carboxylic acid may be at least onecompound selected from the group consisting of compounds having thestructure represented by the formula (2).

The amount of the Lewis acid type catalyst added may be 0.2-2.0 parts byweight based on the weight of the glycol monoester, the reaction timemay be 2-12 hours, the yield of the glycol diester may be 95% orgreater, and the reaction temperature may be 150-250° C.

The distillation column may have 5-20 steps.

The method of the present invention can significantly reduce thereaction time of a glycol diester by properly selecting a reactioncatalyst and utilizing reactive distillation technique to effectivelyseparate reactants and water as a by-product.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawing in which:

FIG. 1 is a schematic diagram of a reactive distillation deviceaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described in greater detailwith reference to the attached drawing.

In an embodiment of the present invention, a reactive distillationdevice capable of simultaneously performing reaction and distillation inan upper portion of which a distillation column is mounted toeffectively separate reaction products and water as a by-product is usedto reduce the reaction time.

FIG. 1 is a schematic diagram of a reactive distillation deviceaccording to an embodiment of the present invention.

A glycol monoester, a linear aliphatic carboxylic acid and a Lewis acidtype catalyst are charged into a reactor 2. Then, the reaction occurs toproduce reaction products and water as a by-product in the reactor 2. Atthis time, the linear aliphatic carboxylic acid which is supplied in anexcessive amount forms an azeotrope with water to move upward through adistillation column 3. The linear aliphatic carboxylic acid and waterpass through a condenser 4 and are divided into an organic layer and anaqueous layer in an oil water separator 6. The organic layer primarilyincluding the linear aliphatic carboxylic acid is returned to thedistillation column 3 through a material cycling line 5 to participatein the reaction again and water is continuously removed through a waterremoval line 7.

In the present invention, the reaction time can be significantly reducedby continuously removing water using the reactive distillation devicewhen the reaction occurs and the selectivity to a glycol diester can bemaximized using the Lewis acid type catalyst. Further, since the linearaliphatic carboxylic acid forms an azeoptrope with water, it is notnecessary to use an another solvent to form an azeotrope with waterwhich is a by-product of the esterification reaction.

The Lewis acid type catalyst may be any catalyst used in the art.Examples of the Lewis acid type catalyst include, but are not limitedto, tetraisopropyl titanate, tetrabutyl titanate, dibutyltin acetate,tin oxalate, phosphoric acid, etc.

A proper reaction time in the reactor 2 is 2-12 hours and may be 4-8hours. When the reaction time is less than 2 hours, the yield of theglycol diester may be reduced to less than 95%. When the reaction timeis greater than 12 hours, the yield of the glycol diester is similar toa desired level, but the reaction time is long, which causes a reductionin productivity.

The yield of the glycol diester is preferably 95% or greater, and morepreferably 95-99.99%.

The amount of the catalyst added is preferably 0.2-2.0 parts by weight,and more preferably 0.4-1.5 parts by weight, based on the weight of theglycol monoester.

When the amount of the catalyst added is less than 0.2 part by weightbased on the weight of the glycol monoester, the reaction rate isreduced. When the amount of the catalyst added is greater than 2.0 partsby weight, the catalyst cost increases without an increase in thereaction rate.

A reaction temperature of the reactor 2 is preferably 150-250° C., andmore preferably 180-230° C.

When the reaction temperature is less than 150° C., the conversion rateis reduced due to decrease in the reaction rate. When the reactiontemperature is greater than 250° C., the reaction solution isdiscoloured.

The distillation column 3 has preferably 5-30 steps, and more preferably5-20 steps, to effectively separate water produced during the reaction.A tray column or a packing column containing a packing material whichshow the same separation efficiency as with the distillation column mayalso be used.

When the number of step is less than 5, effective removal of water isnot achieved, and thus the reaction rate is reduced. When the number ofstep is greater than 30, investment cost and energy increase without anincrease in the reaction rate.

After the reaction is completed, the conversion rate of the glycolmonoester and the selectivity to the glycol diester and the yieldthereof are calculated using Equations 1, 2 and 3:Conversion rate (%)=[1−(the amount of glycol monoester remained afterthe reaction/the amount of glycol monoester added before thereaction)]×100  Equation 1Yield (%)=[(the amount of the resulting glycol diester)/(the amount ofglycol monoester added before the reaction)×(the molecular weight ofglycol monoester/the molecular weight of glycol diester)]×100  Equation2Selectivity (%)=(Yield/Conversion rate)×100.  Equation 3

According to an embodiment of the present invention, there is a glycoldiester represented by formula (3):R³—C(═O)—O—R¹—O—C(═O)—R²  (3)where R¹ is a C₁-C₁₆ alkylidene group, R² is a C₁-C₁₆ alkyl group, andR³ is a C₃-C₁₆ linear alkyl group.

In formula (3), R¹ and R² may be each independently a linear or branchedgroup. Preferably, R¹ is a branched alkylidene, R² is methyl, ethyl,propyl, isopropyl, butyl, isobutyl, pentyl, isopentyl, hexyl or heptyl,and R³ is propyl, butyl, hexyl, heptyl or octyl. More preferably, theglycol diester is 2,2,4-trimethyl-1,3-pentanediol monobutyratemonoisoburyrate, 2,2,4-trimethyl-1,3-pentanediol mono-2-ethylhexanoatemonobutyrate, neopentyl glycol monobutyrate monoisobutyrate orneopentylglycol mono-2-ethylhexanoate monobutyrate.

In the glycol diester represented by formula (3), it is preferred thatR¹ is a 2,2,4-trimethyl-1,3-pentylidene group, R² is a C₁-C₁₆ alkylgroup, R³ is a C₃-C₁₆ linear alkyl group, and R² and R³ have differentsubstituents from each other.

Alternatively, in the glycol diester represented by formula (3), it ispreferred that R¹ is a 2,2,4-trimethyl-1,3-pentylidene group, R² is1-propyl or 2-propyl, R³ is 2-propyl or 1-propyl, and R² and R³ havedifferent substituents from each other.

The glycol diester can be used as a plasticizer, a lubricant, a solvent,etc., but is not limited thereto and can be applied to any otherapplication possible in the art.

Hereinafter, the present invention will be described in more detail withreference to the following Examples. However, these Examples are givenfor the purpose of illustration and are not to be construed as limitingthe scope of the invention.

EXAMPLE 1

In the present Example, a 1 L glass reactor on which a distillationcolumn filled with a packing material was mounted and to which atemperature controlling system was connected was used. 324.4 g of2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, 171.3 g of butyric acidand 3.25 g of tetraisopropyl titanate were charged into the reactor. Thereactor was heated to 230° C. to perform the reaction. Water producedduring the reaction formed an azeotrope with the butyric acid and wascontinuously removed through the distillation column on the reactor. Thebutyric acid separated from water was returned to the distillationcolumn to be used in the reaction. As a result, the conversion rate of2,2,4-trimethyl-1,3-pentanediol monoisobutyrate was 99.6% after 5 hoursand the selectivity to 2,2,4-trimethyl-1,3-pentanediol monobutyratemonoisobutyrate was 95.4%.

EXAMPLE 2

The same experimental procedure as in Example 1 was performed, exceptthat 1.47 g of tetraisopropyl titanate was used. As a result, theconversion rate of 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate was99.3% after 5 hours and the selectivity to2,2,4-trimethyl-1,3-pentanediol monobutyrate monoisobutyrate was 95.2%.

EXAMPLE 3

In the present Example, a 3 L glass reactor on which a 15-step traycolumn with a diameter of 50 mm was mounted and to which a temperaturecontrolling system was connected was used. 1373.5 g of2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, 728.5 g of butyric acidand 13.7 g of tetraisopropyl titanate were charged into the reactor. Thereactor was heated to 230° C. to perform the reaction. Water producedduring the reaction formed an azeotrope with the butyric acid and wasincluded in an aqueous layer to be continuously removed through an oilwater separator on the reactor. An organic layer separated from theaqueous layer was returned to the tray column (first step). As a result,the conversion rate of 2,2,4-trimethyl-1,3-pentanediol monoisobutyratewas 99.5% after 5 hours and the selectivity to2,2,4-trimethyl-1,3-pentanediol monobutyrate monoisobutyrate was 95.3%.

EXAMPLE 4

The same experimental procedure as in Example 3 was performed, exceptthat the reaction time was changed from 5 hours to 4 hours. As a result,the conversion rate of 2,2,4-trimethyl-1,3-pentanediol monoisobutyratewas 99.4% after 4 hours and the selectivity to2,2,4-trimethyl-1,3-pentanediol monobutyrate monoisobutyrate was 95.8%.

EXAMPLE 5

The same experimental procedure as in Example 3 was performed, exceptthat a 10-step tray column was used instead of the 15-step tray column.As a result, the conversion rate of 2,2,4-trimethyl-1,3-pentanediolmonoisobutyrate was 99.2% after 5 hours and the selectivity to2,2,4-trimethyl-1,3-pentanediol monobutyrate monoisobutyrate was 94.8%.

EXAMPLE 6

The same experimental procedure as in Example 3 was performed, exceptthat a 20-step tray column was used instead of the 15-step tray column.As a result, the conversion rate of 2,2,4-trimethyl-1,3-pentanediolmonoisobutyrate was 99.6% after 5 hours and the selectivity to2,2,4-trimethyl-1,3-pentanediol monobutyrate monoisobutyrate was 95.5%.

COMPARATIVE EXAMPLE 1

In the present Example, a 1 L glass reactor equipped with a Dean-Starktrap capable of refluxing an organic layer without a distillation columnwas used. 291.9 g of 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate,154.6 g of butyric acid and 2.91 g of tetraisopropyl titanate werecharged into the reactor. The reactor was heated to 230° C. to performthe reaction. As a result, the conversion rate of2,2,4-trimethyl-1,3-pentanediol monoisobutyrate was 74.7% after 7 hoursand the selectivity to 2,2,4-trimethyl-1,3-pentanediol monobutyratemonoisobutyrate was 92.1%.

The results obtained from Examples 1-6 and Comparative Example 1 wereshown in Table 1. TABLE 1 Comparative Example 1 Example 2 Example 3Example 4 Example 5 Example 6 Example 1 Reaction 5 5 5 4 5 5 7 time (hr)Conversion 99.6 99.3 99.5 99.4 99.2 99.6 74.7 rate (%) Selectivity 95.495.2 95.3 95.8 94.8 95.5 92.1 (%)

As can be seen in Table 1, when glycol diester is prepared using methodsof Example 1-6, the conversion rate and the selectivity to the glycoldiester are very high and the reaction time is significantly reducedcompared to when using the method of Comparative Example 1.

As described above, the method according the present invention canreduce the reaction time for synthesizing glycol diester to 6 hours orless by utilizing reactive distillation technique capable of performingboth reaction and distillation and can obtain the yield of glycoldiester of 95% or greater by using a Lewis acid type catalyst.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A method of synthesizing glycol diester, comprising reacting a linearaliphatic carboxylic acid and a glycol monoester in the presence of aLewis acid type catalyst.
 2. The method of claim 1, wherein afterintroducing the glycol monoester, the linear aliphatic carboxylic acidand the Lewis acid type catalyst into a reactor, (1) the reaction occursto produce reaction products and water in the reactor; (2) an excess ofthe linear aliphatic carboxylic acid forms an azeotrope with waterduring the reaction to be sent to a condenser through a distillationcolumn; (3) the linear aliphatic carboxylic acid and water passedthrough the condenser are divided into an organic layer and an aqueouslayer in an oil water separator; and, (4) the organic layer is returnedto the distillation column through a material cycling line and water inthe aqueous layer is removed through a water removal line.
 3. The methodof claim 1, wherein the glycol monoester is at least one compoundselected from the group consisting of compounds having the structurerepresented by formula (1):HO—R¹—O—C(═O)—R²  (1) where R¹ is a C₁-C₁₆ alkylidene group and R² is aC₁-C₁₆ alkyl group.
 4. The method of claim 1, wherein the linearaliphatic carboxylic acid is at least one compound selected from thegroup consisting of compounds having the structure represented byformula (2):R³—C(═O)—OH  (2) where R³ is a C₃-C₁₆ linear alkyl group.
 5. The methodof claim 1, wherein the amount of the Lewis acid type catalyst added is0.2-2.0 parts by weight based on the weight of the glycol monoester. 6.The method of claim 2, wherein the reaction time is 2-12 hours and theyield of the glycol diester is 95% or greater.
 7. The method of claim 2,wherein the reaction temperature is 150-250° C.
 8. The method of claim2, wherein the distillation column has 5-20 steps.
 9. A glycol diesterrepresented by formula (3):R³—C(═O)—O—R¹—O—C(═O)—R²  (3) where R¹ is a C₁-C₁₆ alkylidene group, R²is a C₁-C₁₆ alkyl group, and R³ is a C₃-C₁₆ linear alkyl group.
 10. Theglycol diester of claim 9, wherein R¹ is a2,2,4-trimethyl-1,3-pentylidene group, R² is a C₁-C₁₆ alkyl group, R³ isa C₃-C₁₆ linear alkyl group, and R² and R³ have different substituentsfrom each other.
 11. The glycol diester of claim 9, wherein R¹ is a2,2,4-trimethyl-1,3-pentyl group, R² is 1-propyl or 2-propyl, R³ is2-propyl or 1-propyl, and R² and R³ have different substituents fromeach other.